Apparatus for stressing semiconductor substrates

ABSTRACT

Apparatus for use in preparing heterostructures having a reduced concentration of defects including apparatus for stressing semiconductor substrates to allow them to conform to a crystal having a different crystal lattice constant.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Divisional of U.S. patent application Ser. No.14/142,559, filed Dec. 27, 2013, which claims the benefit of U.S.Provisional Application No. 61/747,613, filed Dec. 31, 2012; of U.S.Provisional Application No. 61/793,999, filed Mar. 15, 2013; of U.S.Provisional Application No. 61/790,445, filed Mar. 15, 2013 and of U.S.Provisional Application No. 61/788,744 filed Mar. 15, 2013, each ofwhich is incorporated herein by reference.

FIELD OF THE DISCLOSURE

The present disclosure relates generally to apparatus to stress asemiconductor substrate.

BACKGROUND

A continuing need exists for apparatus that may be used to stress asemiconductor structure.

SUMMARY

One aspect of the present disclosure is directed to an apparatus forbending a semiconductor substrate. The substrate has a generally planarposition and a bent position. The apparatus includes a chamber and aheater for heating the chamber. A substrate holder is mounted in thechamber. The holder includes a plurality of spaced-apart elongate pins.Each pin has a support surface for contacting the substrate. The supportsurfaces are disposed for contacting the substrate in the bent position.

In another aspect, an apparatus for bending a semiconductor substrateincludes a chamber, a heater for heating the chamber, a pressuremodulator for causing a pressure differential across the substratesufficient to exert stress on the substrate and a substrate holdermounted in the chamber. The substrate has a front surface, a backsurface and a peripheral edge. The substrate holder includes a frontring and a back ring. Each ring includes an annular support forcontacting the substrate adjacent a peripheral edge of the substrate.The front ring is adapted to contact the front surface and the back ringis adapted to contact the back surface of the substrate.

In yet a further aspect of the apparatus for stressing a semiconductorsubstrate, the apparatus includes a chamber, a heater for heating thechamber and a substrate holder mounted in the chamber. The substrate hasa front surface, a back surface and a peripheral edge. The substrateholder has a front ring, a back ring and a clamp for holding the frontring and back ring. Each ring includes an annular support for contactingthe substrate adjacent a peripheral edge of the substrate. The frontring is adapted to contact the front surface and the back ring adaptedto contact the back surface of the substrate.

In another aspect of the present disclosure is directed to an apparatusfor stressing a generally circular semiconductor substrate. Thesubstrate has a central axis, a front surface and a back surface whichare generally perpendicular to the central axis, a peripheral edgeextending from the front surface to the back surface and acircumferential groove in the back surface adjacent the peripheral edge.The apparatus includes a chamber, a heater for heating the chamber and asubstrate holder mounted in the chamber. The holder includes a generallyplanar back support having an annular boss sized to be received in thegroove in the back surface of the substrate. The boss is movable toexert stress on the substrate.

In a further aspect, an apparatus for stressing a generally circularsemiconductor substrate comprises a chamber, a heater and a substrateholder mounted in the chamber. The substrate has a central axis, a frontsurface and a back surface which are generally perpendicular to thecentral axis. A peripheral edge extends from the front surface to theback surface. The substrate includes a ring bonded to the back surfaceadjacent the peripheral edge. The substrate holder includes a generallyplanar back support having a flange adapted to engage the ring on theback surface of the substrate. The support is movable to exert stress onthe substrate.

A further aspect of an apparatus for bending a semiconductor substrateincludes a chamber, a heater for heating the chamber, a pressuremodulator for causing a pressure differential across the substratesufficient to exert stress on the substrate and a substrate holdermounted in the chamber. The substrate has a front surface, a backsurface and a peripheral edge. The substrate is movable between agenerally planar position and a bent position. The substrate holderincludes a concave-shaped support having a plurality of holestherethrough. The pressure modulator is adapted to pull a vacuum throughthe holes to thereby pull the substrate into the concave-shaped support.

Yet a further aspect of the present disclosure is directed to anapparatus for stressing a semiconductor substrate. The substrate has acentral axis, a front surface and a back surface which are generallyperpendicular to the central axis. A peripheral edge extends from thefront surface to the back surface. The apparatus includes a chamber, aheater for heating the chamber and a substrate holder mounted in thechamber. The holder includes a generally planar back support and a pressfor receiving and compressing the substrate. The press is adapted togenerally uniformly compress the substrate radially inward at itsperipheral edge toward its central axis.

Various refinements exist of the features noted in relation to theabove-mentioned aspects of the present disclosure. Further features mayalso be incorporated in the above-mentioned aspects of the presentdisclosure as well. These refinements and additional features may existindividually or in any combination. For instance, various featuresdiscussed below in relation to any of the illustrated embodiments of thepresent disclosure may be incorporated into any of the above-describedaspects of the present disclosure, alone or in any combination.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of an apparatus for processing asemiconductor substrate according to one embodiment of the presentdisclosure;

FIG. 2 is a perspective view of the apparatus of FIG. 1 with a portionof a chamber removed for clarity;

FIG. 3 is a cross-section view of a substrate holder of one embodimentof the present disclosure;

FIG. 4 is a perspective view of the substrate holder of FIG. 3;

FIG. 5 is a cross-section view of a substrate holder of a secondembodiment of the present disclosure;

FIG. 6 is a perspective view of a tubular pin used in the substrateholder of FIG. 5;

FIG. 7 is a cross-section view of a second embodiment of an apparatusfor stressing a semiconductor substrate;

FIG. 8 is a partial cross-section view of the substrate holder of theapparatus shown in FIG. 7;

FIG. 9 is a partial cross-section view of the substrate holder showing acoating on the peripheral edge of the substrate;

FIG. 10 is a cross-section view of a third embodiment of an apparatusfor stressing a semiconductor substrate;

FIG. 11 is a partial cross-section view of the substrate holder of theapparatus shown in FIG. 10;

FIG. 12 is a partial cross-section view of the substrate holderillustrating movement of the substrate and top ring upon application ofthe holder by arrows;

FIG. 13 is a partial cross-section view of a fourth embodiment of anapparatus for stressing a semiconductor substrate;

FIG. 14 is a cross-section view of a fifth embodiment of an apparatusfor stressing a semiconductor substrate;

FIG. 15 is a cross-section view of a sixth embodiment of an apparatusfor stressing a semiconductor substrate;

FIG. 16 is a cross-section view of the substrate holder of the apparatusshown in FIG. 15;

FIG. 17 is a cross-section view of the apparatus;

FIG. 18 is a cross-section view of the substrate holder of FIG. 18indicating stretching of the substrate by an arrow;

FIG. 19 is a partial cross-section view of a third embodiment of asubstrate holder;

FIG. 20 is a partial cross-section view of an apparatus with thesubstrate support of FIG. 19;

FIG. 21 is a partial cross-section view of the substrate holder of FIG.19;

FIG. 22 is a partial cross-section view of a fourth embodiment of asubstrate holder;

FIG. 23 is a partial cross-section view of an apparatus with thesubstrate support of FIG. 22;

FIG. 24 is a cross-section view of the substrate holder of FIG. 23illustrating the direction of application of the front and back supportby arrows;

FIG. 25 is a cross-section view of another a fifth of a substrateholder;

FIG. 26 is a cross-section view of a sixth embodiment of a substrateholder;

FIG. 27 is a cross-section view of a seventh embodiment of a substrateholder;

FIG. 28 is a cross-section view of a seventh embodiment of an apparatusfor stressing a semiconductor substrate;

FIG. 29 is a cross-section view of an eighth embodiment of a substrateholder;

FIG. 30 is a bottom view of a substrate holder of a tenth embodiment ofa substrate holder;

FIG. 31 is a cross-section view of the substrate holder of FIG. 31;

FIG. 32 is a cross-section view of the substrate holder mounted to amounting block support;

FIG. 33 is a cross-section view of the substrate holder and mountingblock support with a substrate loaded thereon; and

FIG. 34 is a cross-section view of the substrate holder and mountingblock support with a substrate in a stressed position.

Corresponding reference characters indicate corresponding partsthroughout the drawings.

DETAILED DESCRIPTION

Aspects of the present disclosure include apparatus for applying astress to a semiconductor substrate such as a silicon substrate (e.g., awafer). Referring now to FIGS. 1-2, the apparatus 11 may include achamber 31 and a substrate holder 20 having a substrate support 47 forsupporting a semiconductor substrate 49. The illustrated apparatus 11 isa single substrate processing apparatus; however, the apparatus andmethods disclosed herein are suitable for use in other apparatusincluding, for example, multiple substrate processing apparatus.

The apparatus may also include a “stressor” for stressing the substrate.For instance, the stressor or stressor assembly may include one or moreheaters 15 or a pressure modulator 27. The heater 15 may stress thesubstrate by causing the substrate to expand at a rate different thanthe substrate holder (or a portion of the holder) as described below.Alternatively or in addition, the stressor may be pressure modulator 27that imparts a differential pressure across the substrate. These aremerely some examples of possible stressors and others are contemplatedwithin the scope of this disclosure.

The apparatus 11 includes a chamber 31 having an interior space definedin part by walls 33. A perspective of the chamber 31 is shown in FIG. 2with portions of the chamber walls removed to better illustrate theapparatus 11. Within the interior space of the chamber 31 is a substrateholder 20 to support a semiconductor substrate 49. The holder 20illustrated in FIGS. 1-2 is a susceptor 47 but other holder arrangements(e.g., tubes, rings, clamps and the like) are contemplated, some ofwhich are more fully described below. The substrate holder is designatedas 20 in FIGS. 1-2 and as 20 plus a multiple of 100 (120, 220, 320 etc.)in FIG. 3-34).

The chamber 31 may rest on a shaft 9 or other suitable support. Theapparatus 11, such as the shaft 9, may include devices for causing theholder to grasp and/or release the substrate 49, such as suitablecontrol valves and/or hydraulic or pneumatic lines or tensioning cablesand the like. The chamber 31 may include other arrangements than thoseshown herein without departing from the scope of the present disclosure.

The substrate holder or portions of the holder may be generally opaqueto absorb radiant heating light produced by heaters 15 such as highintensity radiant heating lamps that may be located above and below thechamber 31. The holder may be constructed of opaque graphite coated withsilicon carbide. The walls of the chamber 31 may be made of atransparent material to allow radiant heating light to pass into thechamber. For example, the walls of the chamber 31 may be made oftransparent quartz. Quartz is generally transparent to infrared andvisible light and is chemically stable under typical processingtemperatures.

Heaters 15 other than high intensity lamps may be used to provide heatto the chamber 31 such as, for example, resistance heaters and inductiveheaters. In addition or alternatively, the heaters 15 may be includedwithin the interior space of the chamber 31 or may be integral with thechamber walls without departing from the scope of the presentdisclosure. In other words, the heater or heaters may be of any suitabletype, size and shape, and may be disposed inside or outside the chamber.An infrared temperature sensor (not shown) such as a pyrometer may bemounted on the chamber 31 to monitor the temperature of the holder 20 orsubstrate 49 by receiving infrared radiation emitted by the holder orsubstrate. A system controller 5 (FIG. 1) may be used to control variousoperating parameters associated with the chamber 31 including, forexample, stressor control, gas flow rates and chamber temperature andpressure. It should be understood that apparatus and chamber designsother than that shown in FIGS. 1-2 may be utilized without departingfrom the scope of the present disclosure.

In certain embodiments, the apparatus 11 may be configured for and/orinclude structure suitable for applying a stress to a semiconductorsubstrate and, optionally, for depositing a semiconductor material suchas an epitaxial layer on the substrate. In such embodiments, a processgas that includes the semiconductor material may flow into the apparatus11 from a source of process gas, such as a gas cylinder, to a gasmanifold (not shown) and into the chamber 31. Gas may be introduced tothe chamber 31 before, throughout or after processing. The gas may beheated prior to contacting the substrate 49. The process for depositingan epitaxial layer on a surface of the semiconductor substrate mayinclude methods known in the art and as, for example, as described inU.S. Pat. Nos. 5,789,309; 5,904,769 and 5,769,942. Typically, growth ofthe epitaxial layer is achieved by chemical vapor deposition. Generallyspeaking, chemical vapor deposition involves the introduction ofvolatile reactants with a carrier gas (usually hydrogen) into thechamber 31.

Various embodiments of the substrate holder for use in applying a stressto a semiconductor substrate will now be described. Some alternativeembodiments of substrate holders and stressors (e.g., heater, pressuremodulators and the like) for stressing a semiconductor substrate areillustrated below, but other holders and stressors are contemplatedwithin the scope of this disclosure. It should be understood that theholders and stressors may be utilized as a part of the apparatus 11 andchamber 31 described above and may be used in combination with a heaterfor heating the chamber.

Referring now to FIGS. 3-4, a substrate holder 20 may include a numberof spaced-apart elongate pins 22 that support the semiconductorsubstrate 49. The pins 22 are attached to a mounting block 25. A forcemay be applied to the substrate 49 to cause the substrate to move (e.g.,bend) and contact the pins. The pins 22, or the upper portions thereof,may collectively define a support surface that is disposed forcontacting the substrate 49 in the bent (i.e., stressed) position.

The pins 22, or the upper portions thereof, may be arranged in a concavepattern such that upon application of a sufficient force, the substrate22 deforms or bends from its substantially planar shape to conform tothe concave arrangement of the pins. By deforming in this manner, thesubstrate 22 is stressed.

In certain other embodiments, the apparatus includes a pressuremodulator as shown in FIG. 1 (and FIG. 7 below) to create a pressuredifferential across the substrate that is sufficient to exert stress onthe substrate. Other stressors may be used in these embodiments.

As shown in FIGS. 5-6, pins 22′ may be tubular, thereby defining a lumenfor fluid flow. In some embodiments, the pins 22′ are fluidly connectedto a pressure modulator 27 such as a pump for pulling a vacuum. Thevacuum applied to the substrate 49 may pull the substrate toward thepins by a pulling force. For example, variation in distance between thepins and substrate via a concave pattern of the pins may cause differentamounts of pulling force to be applied to portions of the substrate.These differential forces cause stress to be applied to thesemiconductor substrate 49.

The pins 22, 22′ generally support the substrate in the verticaldirection but may be configured so that they do not restrict movement ofthe substrate in horizontal or radial directions. Allowing radialmovement of the substrate during heating allows the substrate to expandradially without causing slip and dislocations. The pins may extendthrough (rather than from) a mounting block and be connected through aseries of conduits as described below and shown in FIGS. 31-35.

Referring now to FIGS. 7-12, in one embodiment of an apparatus forbending a semiconductor substrate, the apparatus includes a substrateholder 120 having a front ring 131 and a back ring 132. The front ring131 includes an annular front support 134 and the back ring 132 includesan annular back support 136 for contacting and supporting the substrate49. Note the front and back rings may have an L-shaped cross-section asshown in FIG. 8. The front ring 131 is generally adapted to contact thefront surface of the substrate 49 at a discrete radial position and theback ring 132 is generally adapted to contact the back surface of thesubstrate 49 at a discrete radial position. The radial position isslightly inward from the substrate edge. The radial position at whichthe front annular support 134 and back annular support 136 contact thesubstrate 49 may be the same as illustrated in FIG. 8 or may bedifferent without departing from the scope of the present disclosure.

Referring to FIG. 10, the apparatus for bending the substrate 49 (e.g.,stressor) may include a pressure modulator 27 such as a pump to cause adifferential pressure across the substrate. In other words, pressure ishigher on one side of the wafer than the other. This differentialpressure stresses the substrate and may bend the substrate. In suchembodiments, the front ring 131 and back ring 132 act as a seal suchthat the differential pressure across the substrate 49 may bemaintained. The pressure modulator 27 may be in fluid communication witha vent 3 that extends through the wall of the chamber 31 to a sealedcavity 4 within the chamber. The differential pressure applied acrossthe substrate 49 may cause the substrate to bend in the direction oflower pressure.

Bending of the substrate 49 may cause surfaces of the substrate to movebetween the front and back rings 131, 132. Further, thermal expansion ofthe substrate 49 (i.e., a thermal expansion greater than the thermalexpansion of the rings 131, 132) may cause the surfaces to move betweenthe rings 131, 132. In one embodiment and as shown in FIG. 9, aprotective coating 137 covers a portion of the substrate 49 and, inparticular, covers the peripheral edges of the substrate. The coating137 may generally be any protective material that protects the waferfrom damage (such as slip and dislocations) while the substrate is heldbetween the rings 131, 132.

Referring now to FIG. 13, a front ring 131′ and back ring 132′ of theholder 120′ may be arranged such that the rings contact the substrate 49near but not at the peripheral edge of the substrate as with the rings130, 131 of apparatus 120 (FIG. 8). The rings 131′, 132′ may be integralwith the lid and/or bottom of the chamber 31′. Vents 3′ may extendthrough the rings 131′, 132′ of the chamber 31′. The vents 3′ may belocated near the center of the substrate 49 and may limit the deflectionof the substrate upon activation of the pressure modulator 27.

The holder 120′ may also include a planar support 126 that supports thesubstrate 49 such as before application of the rings 131′, 132′. Incertain embodiments, the substrate 49 is attached to the planar support126. The planar support may be made of a material that has a differentthermal expansion coefficient than the substrate (i.e., the ringsthermally expand at a different rate than the substrate) to cause thesubstrate to compress or stretch when the support and substrate areheated or cooled.

Referring to FIG. 14, in some embodiments of the apparatus, theapparatus exerts stress on the substrate 49 by use of the thermalexpansion of the substrate. The substrate holder 220 may include a clamp240 including a front ring 231 and a back ring 232 that exerts a holdingforce on the substrate 49. The front ring 231 includes an annular frontsupport 234 and the back ring 232 includes an annular back support 236.The supports 234, 236 contact the substrate 49 at the peripheral edge ofthe substrate and are adapted to contact the front and back of thesubstrate respectively. For example, the substrate holder 220illustrated in FIG. 14 may be used without a pressure modulator. Inshould be noted that the rings, supports, bosses, clamps and the like ofthe various holders described herein may also be moved radially by anymechanical method including use of pneumatics, hydraulics, motors andthe like.

The rings 231, 232 may be constructed of a material that has a differentthermal expansion coefficient than the substrate (i.e., the ringsthermally expand at a different rate than the substrate). The holdingforce of the clamp 240 in combination with the differential expansionrates of the rings 231, 232 upon heating or cooling causes stress in thesubstrate 49. In embodiments where the rings 231, 232 have a largerexpansion coefficient than the substrate 49, the rings cause thesubstrate to stretch radially. In embodiments where the rings 231, 232have a smaller expansion coefficient than the substrate 49, thesubstrate exerts an inward force on the substrate (i.e., compression ofthe substrate) which results in bending of the substrate.

Referring now to FIGS. 15-18, in another embodiment, a substrate holder320 includes a generally planar back support 346 that includes anannular boss 347 that is sized and shaped to be received in a groove 348in the back of the substrate 49. The boss 347 is movable such that itexerts stress on the substrate 49. For instance, the back support 346may be made of a material that expands at a lesser rate than that of thesubstrate 49 upon heating causing compression of the substrate.Alternatively, the back support 346 may be made of a material thatexpands at a greater rate than that of the substrate 49 upon heatingcausing stretching of the substrate.

The substrate holder 320 may also include a front ring and back ring(not shown) with annular supports similar to the front ring 131 and backring 132 shown in FIG. 8 for sealing of the substrate and allowing apressure modulator to create a pressure differential across thesubstrate to stress the substrate. The chamber 31 that contains theholder 320 may include a vent 3 and sealed cavity 4 for application of avacuum or pressure (FIG. 17). The back ring may be interior to the backsupport 346 and the front ring may be aligned with the back ring or maybe sized and shaped to be closer to the peripheral edge of the substratethan the back ring. The substrate may include a coating as shown in FIG.9.

In some embodiments and as shown in FIGS. 19-21, the substrate holder320 also includes a front support 350 having an annular ring 352 thatextends from the front support. The ring 352 exerts a downward force onthe substrate 49 to prevent the substrate from dislodging from the boss347 during compression or expansion of the substrate during heating.Other structures for accomplishing this function are contemplated withinthe scope of this disclosure.

In other embodiments and as shown in FIGS. 22-24, the substrate holder420 includes a back support 446 and boss 447 similar or identical tothat shown in FIGS. 15-21. The substrate holder 420 also includes afront support 451 and a front boss 455 that is sized and shaped to bereceived in a groove 457 in the front surface of the substrate 49. Thefront support 451 may also be made of a material that expands at alesser rate than that of the substrate 49 upon heating causingcompression of the substrate or may be made of a material that expandsat a greater rate than that of the substrate 49 upon heating causingstretching of the substrate.

Referring to FIGS. 25-27, stressing apparatus 520 of this embodimentincludes a planar back support 561 for supporting the substrate 49 and agenerally circular press 560 with a circular opening for receiving andcompressing the substrate. The planar support may extend only partiallytoward the center of the substrate as in FIGS. 26-28 or may extendcontinuously beneath the substrate 49. The press 560 may continuouslyencircle the substrate or, as shown in FIG. 27, may include a pluralityof arc-shaped segments 563 that form the opening for receiving thesubstrate 49. The press 560 and/or segments 563 may be movable inwardrelative to the substrate 49 to compress the substrate. For instance,the press 560 may be moved as a result of being composed of a materialthat expands at a lesser rate than that of the substrate 49 such thatthe press will compress the substrate upon application of heat. Thesubstrate holder 520 may also include front and/or back rings (notshown) to form a seal upon use of a pressure modulator for creating apressure differential across the substrate as described above.

Referring now to FIG. 28, the substrate holder 620 includes a firstconcave-shaped support 670 and a second concave-shaped support 675opposite the first concave-shaped support. The first concave-shapedsupport 670 includes a plurality of holes 671 formed therein for pullinga vacuum through the holes and for pulling the substrate 49 toward thefirst concave-shaped support. An upper portion 677 of the first support670 contacts a portion of the substrate 49 in its unbent position. Alower portion 678 that is generally larger than the upper portion andwhich contains the holes 671 for pulling a vacuum contacts the substratewhen it is in its bent position. A vent 679 is formed in the secondsupport 675 and the support forms a cavity 672 to allow a vacuum to bepulled through the vent and cavity to stress the substrate. The annularsupport 675 generally only contacts the substrate 49 near or at theperipheral edge of the substrate.

Referring to FIG. 29, a substrate holder 720 includes a generally planarback support 781 and a flange 783. The substrate 49 includes a ring 780attached to the back surface of the substrate near the peripheral edgeof the substrate. The flange 783 is adapted to engage the ring 780. Thesupport 781 and flange 783 are movable relative to the substrate tocompress the substrate. For instance, the support 781 and/or flange 783may be moved as a result of being composed of a material that expands ata greater rate than that of the substrate 49 such that the flange 783will stretch the substrate upon application of heat. In embodimentswhere the ring 780 of the substrate is interior to the flange 783 (notshown), the support 781 and/or flange 783 may be moved as a result ofbeing composed of a material that expands at a lesser rate than that ofthe substrate 49 such that the flange 783 will compress the substrateupon application of heat.

FIG. 30 illustrates the bottom of a mounting block 991 of a substrateholder 920. A series of tubes 989 extend through the mounting block 991to a concave-shaped support 992 (FIG. 32). The tubes 989 are connectedvia a series of conduits 990. The mounting block 991 may include ahandling groove 993 for inserting and removing the mounting block fromthe processing chamber 31 (FIG. 1). As shown in FIG. 32, the mountingblock 991 may be supported on a mounting block support 994 within thechamber. A vacuum tube 996 extends through the mounting block support994 and is in fluid communication with the conduits 990 and tubes 989upon insertion of the mounting block into the chamber 31 (FIG. 1). Asubstrate 49 is placed on the mounting block 991 (FIG. 33). Uponapplication of vacuum, the substrate 49 bends toward the concave-shapedsupport 992 causing stress in the substrate (FIG. 34).

Generally, the stress on the substrate may be directed perpendicular tothe axis of the substrate, either by compressing or stretching by use ofthe embodiments of the apparatus shown in, for example, FIGS. 14-27 and29. Alternatively the stress may be directed along or parallel to theaxis of the substrate, such as by use of the embodiments of theapparatus shown in, for example, FIGS. 5, 7-13, 28 and 30-34.

When introducing elements of the present disclosure or the preferredembodiment(s) thereof, the articles “a”, “an”, “the” and “said” areintended to mean that there are one or more of the elements. The terms“comprising”, “including” and “having” are intended to be inclusive andmean that there may be additional elements other than the listedelements.

As various changes could be made in the above apparatus and methodswithout departing from the scope of the disclosure, it is intended thatall matter contained in the above description and shown in theaccompanying figures shall be interpreted as illustrative and not in alimiting sense.

What is claimed is:
 1. An apparatus for stressing a generally circularsemiconductor substrate, the substrate having a central axis, a frontsurface and a back surface which are generally perpendicular to thecentral axis, a peripheral edge extending from the front surface to theback surface, and a ring bonded to the back surface adjacent theperipheral edge, the apparatus comprising: a chamber, a heater forheating the chamber, a substrate holder mounted in the chamber, theholder including: a generally planar back support having a flangeadapted to engage the ring on the back surface of the substrate, thesupport being movable to exert stress on the substrate.
 2. The apparatusas set forth in claim 1 wherein the back support is made of a materialthat expands at a greater rate than that of the substrate such that heatapplied to the substrate and support will cause stretching of thesubstrate.
 3. The apparatus as set forth in claim 2 wherein the flangeis interior to the ring.
 4. The apparatus as set forth in claim 1wherein the back support is made of a material that expands at a lesserrate than that of the substrate such that heat applied to the substrateand support will cause compression of the substrate.
 5. The apparatus asset forth in claim 4 wherein the ring is interior to the flange.
 6. Theapparatus as set forth in claim 1 further comprising a front supportdisposed adjacent the front surface of the substrate.
 7. The apparatusas set forth in claim 1 further comprising a pressure modulator forcausing a pressure differential across the substrate sufficient to exertstress on the substrate, the substrate holder further including: a frontring and a back ring, each ring including an annular support forcontacting the substrate at a discrete radial position adjacent aperipheral edge of the substrate, the front ring adapted to contact thefront surface and the back ring adapted to contact the back surface ofthe substrate.
 8. The apparatus as set forth in claim 7 wherein thefront and back rings are adapted to form a seal with the substrate tofacilitate causing a pressure differential across the substrate.
 9. Theapparatus as set forth in claim 7 wherein the annular support includes asubstantially sealed cavity and a single vent, the support adapted tocontact one of the surfaces of the substrate and form a seal therewith,the vent enabling a vacuum to be pulled through the cavity for exertingstress on the substrate.
 10. The apparatus as set forth in claim 1 incombination with the substrate, the substrate including a coatingdisposed adjacent the peripheral edge.
 11. The apparatus as set forth inclaim 1 wherein the chamber is an epitaxial chamber for applying anepitaxial layer.